Match an argument to a character vector

This is equivalent to base::match.arg() with a few differences:

• Partial matches trigger an error.

• Error messages are a bit more informative and obey the tidyverse standards.

arg_match() derives the possible values from the caller frame.

arg_match0() is a bare-bones version if performance is at a premium. It requires a string as arg and explicit character values. For convenience, arg may also be a character vector containing every element of values, possibly permuted. In this case, the first element of arg is used.

arg_match(
  arg,
  values = NULL,
  ...,
  multiple = FALSE,
  error_arg = caller_arg(arg),
  error_call = caller_env()
)

arg_match0(arg, values, arg_nm = caller_arg(arg), error_call = caller_env())

Arguments

arg	A symbol referring to an argument accepting strings.
values	A character vector of possible values that arg can take.
...	These dots are for future extensions and must be empty.
multiple	Whether arg may contain zero or several values.
error_arg	An argument name as a string. This argument will be mentioned in error messages as the input that is at the origin of a problem.
error_call	The execution environment of a currently running function, e.g. caller_env(). The function will be mentioned in error messages as the source of the error. See the call argument of abort() for more information.
arg_nm	Same as error_arg.

Value

The string supplied to arg.

See also

arg_require()

Examples

fn <- function(x = c("foo", "bar")) arg_match(x)
fn("bar")
#> [1] "bar"

# Throws an informative error for mismatches:
try(fn("b"))
#> Error in fn("b") : 
#>   `x` must be one of "foo" or "bar", not "b".
#> ℹ Did you mean "bar"?
try(fn("baz"))
#> Error in fn("baz") : 
#>   `x` must be one of "foo" or "bar", not "baz".
#> ℹ Did you mean "bar"?

# Use the bare-bones version with explicit values for speed:
arg_match0("bar", c("foo", "bar", "baz"))
#> [1] "bar"

# For convenience:
fn1 <- function(x = c("bar", "baz", "foo")) fn3(x)
fn2 <- function(x = c("baz", "bar", "foo")) fn3(x)
fn3 <- function(x) arg_match0(x, c("foo", "bar", "baz"))
fn1()
#> [1] "bar"
fn2("bar")
#> [1] "bar"
try(fn3("zoo"))
#> Error in fn3("zoo") : 
#>   `x` must be one of "foo", "bar", or "baz", not "zoo".
#> ℹ Did you mean "foo"?